1. Field of the Invention
The present invention relates to a process for removing precious metals from strongly acidic solutions like manufacturing and waste solutions.
2. Description of the Prior Art
At the present time, the known methods of recovering precious metals such as gold, platinum and palladium from strongly acidic manufacturing solutions and waste solutions are usually very time-consuming and involve a number of processing steps. As an illustration of such processes, see pages 298-299 of Hampel, C. A., Rare Metals Handbook, Reinhold Publishing Company (1956) which show one such multi-step recovery process. In essence, these methods of recovering precious metals from acidic solutions resemble quantitative analysis procedures employed in laboratories.
Furthermore, these procedures are not very efficient when employed on large commercial scales. Also, the difficulty of recovery is always increased when more than one precious metal is present in the acidic solution, or when base metals like iron, copper or tin are additionally present.
Still further, the loss of precious metal values is tolerated in some operations rather than having to transport these strongly acidic solutions to suitable metal recovery facilities. Such transportation is costly and may be hazardous. Accordingly, there is a need in the art of precious metal recovery for a means for easily, efficiently and selectively removing precious metals from strongly acidic solutions. The process of the present invention offers a solution to that need.
Separately, it is known that the zinc chelate of 2-mercaptopyridine-N-oxide will transchelate with other metal ions like iron, copper, mercury and silver. See Olin Corporation Zinc Omadine.RTM. and Sodium Omadine.RTM. Product Data Bulletin (1978). Further, it is also known that the ferric chelate of 2-mercaptopyridine-N-oxide will transchelate with mercury and this reaction is useful for the analytical determination of mercury in solutions. See Edrissi, M., et al; Microchemical Journal, Vol. 15, pages 579-584 (1970). Also, it is known that sodium salt of 2-mercaptopyridine-N-oxide is a selective absorptiometric reagent for the determination of palladium in an alkaline solution and in the presence of masking agents. See Edrissi, M., et al; Microchemical Journal, Vol. 16, pages 177-183 (1971). Still further, U.S. Pat. No. 3,992,506 teaches that alkali metal (e.g., sodium) salts of 2-mercaptopyridine-N-oxide will react with silver in waste plating solutions and form the water insoluble silver salt of 2-mercaptopyridine-1-oxide and this precipitate can be separated from the solution.